in vitro culture and isoenzyme analysis of giardia lamblia

features noted in human infections.
1.5.5 Identification of virulence determinants of the organism which would
help in new drug and vaccine design.
IgA 1 protease activity (cleaving IgA 1 immunoglobulin and haemoglobin) has been
described in Giardia intestinalis trophozoites (Webster, 1980; Parenti 1989)
suggesting that Giardia species can survive in the intestine by degrading host IgA.
The protease activity may be a non-specific virulence factor that allows the
organism to evade host enteric defence mechanisms.
A trypsin-activated, mannose-binding lectin which mediates adherence of the
parasite to host epithelia has been demonstrated on the surface of Giardia
trophozoites (Lev et al., 1986). Whether absence or inhibition of these binding
molecules could prevent parasite colonisation and thus interfere with production of
clinical illness has yet to be investigated.
Giardia has been found to display a large degree of diversity in its surface
antigens (Adam et al., 1988; Aggarwalet al., 1989 Nash et al., 1988; 1990). These
antigens represent a distinct family of cysteine-rich proteins termed variant-specific
surface proteins (VSPs), which cover the entire surface of trophozoites including
the f1agella (Nash, 1992). The trophozoites can vary their surface antigens and
rates of change of VSPs vary markedly among isolates (Nash et al., 1988). These
surface antigens appear to play a role in pathogenecity (virulence) of different
isolates of Giardia:
• The documented differences in resistance to proteases (trypsin and
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